1. Field of the Invention
The present invention relates to a reactive power compensator that generates reactive power to suppress voltage fluctuations of a power system, and a control device for controlling the reactive power compensator.
2. Description of the Related Art
Stabilizing control systems that can stabilize system voltage are known in the art. Japanese Patent Application Laid-Open No. H5-274049, for example, discloses a conventional system that uses a static var compensator (SVC) that controls a switching semiconductor element and can generate “leading” or a “lagging” reactive power instantly. In Japanese Patent Application Laid-Open No. H5-274049, a system that controls an operation of a generator that is operated in the system to an increasing direction is adopted. The system is controlled under a condition that reactive power supplied to the system by the SVC goes over a rating capacity of the SVC and exceeds a predetermined fixed value for a certain period of time. Accordingly, the system voltage set by the SVC is stabilized and maintained, thereby contributing to the stabilization of the system voltage.
Japanese Patent Application Laid-Open No. H10-268952 discloses another stabilizing control system. In the system of Japanese Patent Application Laid-Open No. H10-268952, in addition to the SVC, a capacitor, a reactor, and the like (hereinafter, collectively referred to as “phase modifying equipment”) are used. The phase modifying equipment are connected to a power system interposing a switch therebetween. In Japanese Patent Application Laid-Open No. H10-268952, the system performs control so that a sum of the reactive power generated by the SVC and the reactive power generated by the phase modifying equipment becomes a required amount to suppress a voltage fluctuation. Accordingly, an adjusting range of the reactive power is enlarged, thereby contributing to the stabilization of the system voltage.
In the system that controls the voltage of the generator as indicated in Japanese Patent Application Laid-Open No. H5-274049, it is assumed that the SVC is located near the generator. This system enables to control the reactive power by closely controlling the generator, without closely controlling the SVC. Therefore, if the generator is located near the SVC, it is not too much to say that there is no need to improve the function of the SVC significantly.
When the SVC and the generator are located away from each other, the generator which is at a remote place as seen from the SVC is required to be controlled from a location of the SVC. This makes the control system complicated and increases the costs. Also, when controlling the generator, it is possible that other electrical transmission facilities are affected. Thus, it is not possible to control the reactive power alone.
Meanwhile, the control system disclosed in Japanese Patent Application Laid-Open No. H10-268952 can control the reactive power by utilizing characteristics of the SVC. However, when an electrical transmission facility at a remote place does not have phase modifying equipment, or even if it does have phase modifying equipment, when control elements of the phase modifying equipment are used up, a problem occurs that the voltage at the electrical transmission facility at the remote place cannot be preferentially controlled.